The push to store renewable energy in massive salt caverns

An electrolyzer sits on a truck bed at the Advanced Clean Energy Storage project being constructed in Delta, Utah.
An electrolyzer sits on a truck bed at the Advanced Clean Energy Storage project being constructed in Delta, Utah.


Renewable power is used to produce hydrogen, which is stored in underground caverns until it is needed for green energy.

On a plain in western Utah, two massive caverns—each roughly big enough to house the Empire State Building—are being hollowed out of rock salt a mile underground.

Salt caverns like these are emerging as one possible solution to the question of how to store solar and wind energy for later use.

It’s a three-step process. First, electricity from solar and wind farms is used to produce hydrogen. Then the hydrogen is stored in caverns like those scheduled to be completed next year at the Advanced Clean Energy Storage project in Delta, Utah. Finally, the hydrogen can be used as a green substitute for climate-warming fossil fuels in uses ranging from power generation to steel manufacture and shipping.

A number of companies in the U.S. and Europe have started to invest in or seriously study salt-cavern projects in the past few years, with government subsidies for clean energy spurring them on.

Cost considerations

Countries around the globe are building huge amounts of wind and solar energy capacity. In the U.S., around 21% of power generated comes from renewable sources now, but the government is aiming for a zero-carbon power grid by 2035, with heavy reliance on renewables to achieve that goal.

The problem is that renewable power generation can fluctuate a lot depending on the time of day or year. Solar-panel output, for instance, stops when the sun sets, and in California can roughly halve in winter versus summer.

Utilities are building big battery installations that can suck up some of that renewable electricity when it’s plentiful during the day, and release it for a few hours in the evening. But the lithium-ion batteries most commonly used today are too small and expensive to absorb the massive amounts of power needed to balance out grids over months or seasons, energy-industry executives say.

Capturing that renewable power by making hydrogen with it and storing the gas underground isn’t cheap. Industry executives say the cost to make a salt cavern could easily exceed $100 million, on top of expenses for the equipment needed to produce the hydrogen. But trying to provide similar storage with batteries is much pricier.

Green Hydrogen International, a company planning a cavern project in South Texas, estimates it would take around 38,500 Tesla Megapacks—a type of battery popular for large-scale utility installations—at an estimated cost of $59 billion to store the amount of energy it is hoping to keep in its caverns, which it estimates will cost $150 million to make.

And just one of the ACES Delta caverns in Utah will be able store more than three times as much energy as all of the utility-scale batteries the U.S. had online at the end of 2023.

Those economics were good enough to attract the interest of Japanese oil-and-gas company Inpex, which is joining GHI in a feasibility study of the Texas project. “What we’re trying to do is take renewables and make them oil-and-gas scale," says Brian Maxwell, GHI’s chief executive. “You think of (the caverns) as a big underground battery."

Room to grow

Salt caverns have been used since at least the 1940s to store fossil fuels. The U.S. keeps a good portion of its natural gas underground, as well as its emergency crude-oil reserves, which reside in four huge salt caverns in Texas and Louisiana.

The caverns are typically hollowed out of deposits of rock salt, formed from the remnants of ancient seas that have hardened into layers or been squeezed into pillars or mushroom-shaped domes of salt underground.

Salt deposits have advantages for storing hydrogen, a notoriously tough gas to trap. They are more leakproof than other types of rocks used for storage sites—a feature especially important for hydrogen, which is the smallest molecule in existence. And the rock salt doesn’t react with hydrogen, which can be corrosive to tanks when it is stored above ground.

To create a cavern, engineers drill deep down into a salt deposit, then flush it with massive amounts of water, which slowly erodes the salt and forms a long, tubelike hole, a process that can take two or three years.

Some rock-salt domes in the U.S. are more than a mile in diameter and are capable of housing more than a hundred storage caverns, says Scyller Borglum, vice president for underground storage at engineering firm WSP Global, and deputy project manager for salt-cavern construction at ACES Delta.

That scale will be necessary if hydrogen becomes a significant energy source, versus its current main use in fertilizers and refining. If the U.S. clean-hydrogen market grows to around 10% of the size of the country’s natural-gas market as measured by energy output, more than a thousand new salt caverns will be needed for hydrogen storage, says Mark Shuster, a researcher at the Bureau of Economic Geology at the University of Texas, Austin, who oversees a program studying underground storage for the gas.

Storage starts next year

Michael Ducker, board director of ACES Delta and an executive at a unit of Japan’s Mitsubishi Power, says he got involved in the project in 2019, when the Intermountain Power Agency, owner of a big Utah coal-power plant that supplies electricity to southern California, approached Mitsubishi Power with a plan to replace the plant with one powered by natural gas and hydrogen. The idea was to use the ballooning amount of excess electricity generated by West Coast solar and wind farms—energy that is now unused—to run electrolyzers, equipment that produces hydrogen by separating it out of water. Mitsubishi Power decided to invest in the project and supply turbines for the new plant.

Luckily, the power plant was next to a big salt dome, which already housed caverns for storing natural gas. ACES Delta started drilling for its hydrogen caverns in 2022 and pumping in water last year. It will begin replacing the water in the caverns with hydrogen next year, Ducker says.

When completed, ACES Delta will be the biggest hydrogen-storage site in the world, and one of the few large-scale green hydrogen projects to get off the ground so far. In a sign of the intense interest the project has generated, U.S. energy giant Chevron bought one of the project partners last year, and now holds a majority stake.

Phred Dvorak is a Wall Street Journal reporter in Houston. She can be reached at

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